In recent years, a storage system including a nonvolatile memory has been proposed. In this type of storage system, a separate controller other than a controller that controls read and write of data copies data stored in a nonvolatile memory chip in which a failure has occurred to another nonvolatile memory chip (for example, Japanese Laid-open Patent Publication No. 2008-191966). Also, in this type of storage system, while the life of a nonvolatile memory is managed, data stored in a hard disk drive is moved to the nonvolatile memory, thereby reducing power consumption of the entire storage system (for example, Japanese Laid-open Patent Publication No. 2007-115232).
It has been known that, in a storage system, as the data write amount increases, the access efficiency reduces. For example, in a storage system including a hard disk drive, as a result of repeating of write and deletion of a file, fragmentation of a file occurs, and the access speed is reduced. On the other hand, in a nonvolatile memory, such as a flash memory and so forth, data is erased in a unit of block before data is rewritten. Thus, in a storage system including a nonvolatile memory, such as a flash memory and so forth, as the write data amount increases, the throughput of a write operation reduces.
However, there has not been any proposed method yet in which, while increase in load of a system is reduced, the performance of a storage system, which has been degraded by reduction in access efficiency and so forth, is recovered.